Three Dimensional Low-Tortuosity Carbon Fibers Enable High-Areal-Capacity and Long-Durability Battery

Abstract

Increasing the thickness of lithium-ion battery electrodes enables significant improvement in energy density and reducing the manufacturing cost. However, the existing barriers such as manufacturing challenges, performance issues, and scalability impede the development of fabricating thick electrodes. Here, we demonstrate a three dimension, low-tortuosity, and metal current collector free carbon fiber (CF) electrode which works as an integrated host substrate for LiNi0.5Mn0.3Co0.2O2 (NMC 532) cathode materials, similarly, the paired anode. The low tortuosity (~ 1.7) aligned microchannels of CF provide a good electron conductivity (~ 0.23 S cm-1), low Li+ diffusion resistance (~ 22 Ω), and high reversibility (91% over 500 cycles at C/3) compared to ~ 0.01 S cm-1, ~ 34 Ω, and 50% over 50 cycles for 100 µm slurry-casting graphite electrode with tortuosity of 2.9, respectively. The large porosity (~ 60%) enables CF a high mass loading capability of NMC 532 (> 70 mg cm-2) which provides a theoretical areal capacity ~ 14 mAh cm-2. The practical design of NMC 532/CF versus CF thick cells, with NMC 532 mass loading 32 mg cm-2, and theoretical areal capacity ~ 5.5 mAh cm-2 show an initial discharge areal capacity 4.1 mAh cm-2 at C/3 (1.5 mA cm-2), a capacity retention of 90.4% (500 cycles), 78.1% (1000 cycles), and 65.5% (1500 cycles). Furthermore, the post-analysis of long-term cycled NMC 532 particles, with consistent morphology of pristine particles, demonstrates lessen thermal stress across the electrodes. Our work presents a well-aligned microstructure for thick lithium-ion electrodes with practical level, scalable manufacturing, high areal capacity, and long-term electrochemical durability.